FOSSILS OF OLD RED SANDSTONE. 55 



be no fossil remains indicating a transition from 

 the lower animals to fish. The reviewer speaks 

 of a recently discovered cestraceon below any 

 other fish-beds in England. " Such," he exclaims, 

 •' are nature's first abortive efforts." " We en- 

 treat," he adds, " any good naturalist well to con- 

 sider such facts as these, and tell us whether they 

 do not utterly demolish everj- attempt to derive 

 such organic structures fi'om any inferior class of 

 animal life found in the older strata ?" Now, I 

 cannot tell what good naturalists may say in 

 answer to this appeal ; but I feel, for my own part, 

 that the facts in question — as far as they can be 

 admitted to be so — have no such destructive 

 effect. 



In the first place, the cestraceon is only one 

 of those cartilagines, the real character of which 

 had just been explained. It is not the lowest of its 

 order, but neither is it the highest. So far fi-om this 

 being the case, the respiration of the whole family 

 (Selacii, Cuv. ; Plagiostomi, Desm.) to which it 

 belongs, and which also includes sharks, is per- 

 formed in a manner which approximates these 

 fishes to the worms and insects — namely, " by 

 numerous vesicles called internal gills, the en- 

 trance to which is from their gullet, while the exit 



